1. Field of the Invention
The present invention relates to a multilayer capacitor which is suitably used for decoupling circuits and the like for supplying electric power from a power source to circuitry such as IC (Integrated Circuit).
2. Description of Related Art
A decoupling circuit is a circuit which is connected between an IC and a power source for suppressing fluctuations in voltage by rapidly charging or discharging in response to fluctuations in electric current supplied from the power source to the IC.
The function to rapidly charge or discharge electric current is attained by decreasing impedance of the decoupling circuit.
A desirable decoupling circuit has electrical characteristics with a wide frequency band in which impedance is low (referred to as “effective frequency band”). Owing to this, current fluctuations including those occurring at low frequencies as well as those occurring at high frequencies can be suppressed. Such a decoupling circuit can be constructed by connecting a plurality of capacitors each having a different “effective frequency band” in parallel.
The following is one example of conventionally known multilayer capacitors used for decoupling circuits.
A multilayer capacitor comprises a multilayer body including a plurality of dielectric layers laminated together, a plurality of first internal electrodes and second internal electrodes that are disposed alternately so as to be opposed to each other with the dielectric layers interposed in between, first extension portions and second extension portions are extended to lateral sides of the multilayer body at a plurality of locations. The first extension portions and second extension portions located vertically in the stacking direction are electrically interconnected, respectively, thereby to form a first terminal electrode and a second terminal electrode along the stacking direction on the lateral sides of the multilayer body (See WO99/00807, for example).
In the foregoing multilayer capacitor, the equivalent series inductance is minimized by forming a plurality of extension portions extended from internal electrodes so as to shorten the current flow path. Accordingly, it has electrical characteristics with the series resonance point shifted to the higher frequency side. Since an area in the vicinity of this series resonance point corresponds to the “effective frequency band”, such a multilayer capacitor is allowed to function on the higher frequency side when used for a decoupling circuit.
The multilayer capacitor used for a decoupling circuit is preferably one with an “effective frequency band” which covers a wide frequency range. For example, the foregoing multilayer capacitor in which the number of extension portions is increased has a smaller equivalent series inductance and an “effective frequency band” that is extended on the higher frequency side.
However, in such a multilayer capacitor, due to the lowered equivalent series inductance, the impedance at the series resonance point is greatly decreased. For this reason, the impedance at the parallel resonance point created with another capacitor in the decoupling circuit is high, which sometimes causes the decoupling circuit to have electrical characteristics in which the impedance is higher than the standard value in a specific frequency band.
As described above, when a multilayer capacitor with a wide “effective frequency band” is employed for a decoupling circuit, the problem of too high impedance at the parallel resonance point created with another capacitor is prone to arise.
It is therefore an object of the present invention to provide a multilayer capacitor with a wide “effective frequency band” with which it is possible to suppress the impedance at the parallel resonance point created with another capacitor in a decoupling circuit.